No single, conventional treatment has been shown to significantly benefit adults with anorexia nervosa (AN), which ranks among the leading causes of disability and premature death in young women. We propose to test the hypothesis that a novel, couple-based intervention developed for adult AN (UCAN [Uniting Couples (in the treatment of) Anorexia Nervosa]) developed under RFA-MH-07-090 significantly enhances treatment outcome and reduces risk of relapse compared with treatment conducted entirely on an individual basis, the standard mode of treatment delivery in the community. This application, submitted in response to PA-10-067 Research Project Grant (Parent R01) will further establish the efficacy of UCAN. UCAN mutually engages patients and partners in reducing the psychopathology of AN and its impact on relationship functioning. Encouraging results from our pilot - significant weight gain and unprecedentedly low treatment drop out - support this application. In order to determine whether UCAN is superior to individual treatment alone, we propose a randomized controlled trial comparing: 1) UCAN plus individual cognitive-behavioral therapy (UCAN+CBT) to 2) Individual CBT. All patients receive the same core of interventions used in conventional AN treatment, specifically: 1) medical management, 2) nutrition counseling, and 3) individual CBT. Further, participants will be randomly assigned either to: 1) UCAN or 2) a higher dose of individual CBT. The design addresses a question of clinical, developmental, and conceptual importance heretofore unexplored: Is treatment of adult AN optimized when it includes active participation of the patient's partner, compared with the community standard of individual therapy only. The primary aims are to compare the efficacy of UCAN+CBT with Individual CBT in: 1) increasing BMI and improving global clinical improvement, and 2) increasing retention in and satisfaction with treatment. Exploratory aims will address whether: 1) evidence exists to suggest that improvement in primary outcome variables may be partially mediated by improvements in relationship functioning and patient readiness to change; and 2) illness duration, subtype (restricting vs. binge/purge), and baseline level of emotion dysregulation should be considered as candidate moderators of treatment outcome in subsequent trials. We will collect data to guide the design of a more comprehensive cost-effectiveness analysis if a subsequent multi-site trial is warranted. The primary outcomes are change in BMI, global improvement, retention, and treatment satisfaction. We will recruit 50 couples (40 completers) over 3.75 years and follow all patients for one year. The Data Monitoring Group (DMG) will monitor recruitment, treatment fidelity, assessments, and human subject protections. Results from this trial will guide future, more definitive trials and inform therapeutic perspectives guiding the treatment of adults with AN. The development of innovative, efficacious treatments for adult AN is essential to reducing the chronic morbidity, high risk of mortality, and substantial personal, familial, and public health burdens incurred by this debilitating and recalcitrant illness.